1. Field of the Invention
The present invention relates to an angle detecting apparatus using one or more range finders, and to a projector having the same.
2. Description of Related Art
In a conventional projector, such as a liquid-crystal or DLP projector, there is a type of distortion known as a keystone distortion which appears as a distorted shape of an image caused by an improper positional relationship between the projector and the viewing screen. In keystone distortion, one side of the projected image is typically larger than the opposite side. There are generally two methods of optical correction used for correcting keystone distortion, including an electric correction method in which an image generated by a video circuit is projected with a keystone distortion inverse to the projected image, and an optical correction method in which the tilt of a condensing lens contained within a projection optical system of the projector is corrected without correcting the image created by the video circuit.
A known technique that uses a range finder to automatically correct such a keystone distortion is described in, for example, JP-A-2000-122617. The technique described therein comprises the steps of detecting the distance to the screen using two active range finding sensors mounted at different locations in front of a liquid crystal projector, calculating one inclination angle of the liquid crystal projector with respect to the screen based on the two detected distances and on the distance between the two range finding sensors, and correcting the keystone distortion based on the calculated inclination angle by the aforementioned method.
In the technique described in JP-A-2000-122617, only one inclination angle of the liquid crystal projector with respect to the screen is detected from only two range finding results. Therefore, there is the problem that if one or both of the two range finding results are not reliable due to noise or the like during range finding calculation, then the accuracy at which the inclination angle is detected deteriorates.